Hydroxamic acid derivatives with tricyclic substitution, as shown in formula (X) below, are known for their pharmacological activity as cartilage protective agents and are particularly useful in the treatment and prevention of degenerative joint diseases such as atherosclerosis (U.S. Pat. No. 5,614,625, EP 684 240 A1).
Certain chiral succinic acid derivatives, as shown in formula (I) below, are valuable intermediates in the synthesis of the above compounds (EP 816 341 A1). Since these derivatives are chiral, it is important to develop a stereoselective reaction to most efficiently obtain the desired enantiomer. It is known that lithium bases such as LDA provide syn-selectivity (in ratios of up to 90:10) in reactions with succinic acid derivatives with an ester group and a free acid group (R. Becket et al., Synlett. 137, February 1993). However sodium bases such as NaN(TMS).sub.2 are not specific, providing a 1:1 mixture of syn to anti addition products.